The present invention relates to a gear wheel construction. More particularly, the gear wheel construction of the present invention is intended for use in gear systems adapted to allow changing of gears under load without the need for a traditional clutch and with the substantial minimisation of any momentary reduction in power input to the system.
Constant mesh gear boxes generally rely on a means to lock and unlock individual gears with respect to a drive shaft. Unlocking a gear disengages that gear ratio and allows the gear to rotate freely about the shaft. Conversely, locking a gear with respect to the shaft causes that gear ratio to be engaged.
This sequence allows transmission of power from the shaft in respect of which that gear has been locked to another shaft about which a complimentary gear is provided in fixed or locked relation, at that gear ratio. Such gear pairs or ratios are generally in constant mesh aligned along the length of two substantially parallel shafts. One gear pair or ratio is engaged at any one time whilst the remaining gear pairs or ratios rotate freely about the shaft.
The applicant""s co-pending International Patent Application PCT/AU98/00181 discloses a gear system wherein gears may be changed under load by engaging the next desired gear whilst the presently engaged gear remains engaged also. The newly engaged gear assumes the load from the previous gear allowing that previous gear to unlock freely from its shaft.
This gear system may present a problem when a user wishes to change xe2x80x9cdownxe2x80x9d through gears when under load as the previously engaged gears only unlock upon subsequent engagement or pre-loading of a gear wheel that causes the driven shaft to rotate more quickly. A xe2x80x9cdownxe2x80x9d gear change from a xe2x80x9ctallxe2x80x9d or high gear to a xe2x80x9cshorterxe2x80x9d or lower gear does not allow that xe2x80x9ctallxe2x80x9d gear to disengage from the shaft.
The gear wheel construction of the present invention has as one object thereof to overcome the above problems associated with the prior art.
Throughout the specification, unless the context requires otherwise, the word xe2x80x9ccomprisexe2x80x9d or variations such as xe2x80x9ccomprisesxe2x80x9d or xe2x80x9ccomprisingxe2x80x9d, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.
In accordance with the present invention there is provided a gear wheel construction for use in a constant mesh gear box, the gear wheel construction characterised by a single gear wheel provided about a shaft in a rotatable and engageable manner, the gear wheel being divided longitudinally (axially) into two components, the first being a synchro-gear wheel and the second gear being a partially toothed gear wheel, wherein the synchro-gear wheel is provided in constant mesh with a gear wheel forming its gear wheel pair whilst the partially toothed gear wheel is meshed therewith intermittently during rotation, the synchro-gear wheel and the partially toothed gear wheel having provided therebetween at least one biasing means allowing momentary asynchronous rotation therein.
Preferably, the synchro-gear wheel is provided about its shaft in a rotatable manner only, the partially toothed gear wheel alone being able to releasably engage the shaft.
Still preferably, the or each biasing means act to draw the partially toothed gear wheel and synchro-gear wheel into synchronous rotation after any momentary asynchronous rotation. The force required to disengage the partially toothed gear wheel from its shaft is preferably greater than the force exerted thereon by the or each biasing means.
In accordance with the present invention there is further provided a gear system characterised by a pair of substantially parallel shafts, each shaft having provided thereabout at least two gear wheels forming gear wheel pairs or ratios with those gear wheels on the other shaft, wherein a rotary force applied to one shaft may be transferred to the other shaft through the gear wheels associated therewith upon that gear wheel pair being engaged with the shaft, wherein at least one of the gear wheel pairs has one gear wheel of that pair divided longitudinally (axially) into two components, the first being a synchro-gear wheel and the second gear being a partially toothed gear wheel, wherein the synchro-gear wheel is provided in constant mesh with a gear wheel forming its gear wheel pair whilst the partially toothed gear wheel is meshed therewith intermittently during rotation, the synchro-gear wheel and the partially toothed gear wheel having provided therebetween at least one biasing means allowing momentary asynchronous rotation therein.
In accordance with the present invention there is still further provided a method of changing down from a tall or higher gear to a shorter or lower gear in a constant mesh gear system under load, the method characterised by the method steps:
calling for a down gear change;
simultaneously disengaging the taller gear from the shaft and engaging a gear wheel comprising both a synchro-gear wheel and a partially toothed gear wheel, asynchronous rotation of the partially toothed gear wheel with respect to the synchro-gear wheel allowing the taller gear to unlock; and
engaging the shorter gear with the shaft.
The method of the present invention preferably further provides for the partially toothed gear wheel to return to synchronous rotation with the synchro-gear wheel. Such may be achieved through the action of a biasing means provided between the synchro-gear wheel and the partially toothed gear wheel.
The method of the present invention may be achieved, in bicycles, through use of a hand controller to cause momentary engagement of the gear wheel incorporating the partially toothed gear wheel.
Preferably, the method of the present invention may be put into effect by way of a form of programmable logic controller, microprocessor, computer, or engine management system. The step of calling for a change in gear may be initiated automatically by the programmable logic controller, microprocessor, computer, or engine management system or may be initiated manually.
For bicycles, the gear system of the present invention can be incorporated into a chainless drive shaft between the crank and the rear wheel. The system may be fitted with a dual rear bevel gear and a dual direction rear wheel ratchet/roller clutch to provide power during back pedalling. This arrangement allows step pedalling and allows the rider to power forwards by alternately shifting his weight from one foot to the other whilst standing upon the pedals of the bicycle. This arrangement allows power to be maintained while the rider is negotiating rough or otherwise difficult terrain. Alternatively, the gear system may be provided with a rear foot brake. It is envisaged that a dual ratchet or full lock pawl arrangement for engagement of the gear wheels would be required for step pedalling or rear foot braking.